1. Field of the Invention
This invention relates to spot weld removal and more particularly to a spot weld drill that uses a pneumatically actuated piston for providing cutting pressure for a drill bit.
2. Description of the Related Art
A spot weld is a commonly used technique for holding two pieces of sheet metal or other material together. A spot weld is formed by placing two pieces of sheet metal in facing contact with each other and connecting the two sheets into an electric welding circuit. Two small diameter cylindrical electrodes are placed on opposite sides of the position to be welded. The two surfaces to be welded are compressed together by the electrodes as electrical current is passed between the electrodes to heat the spot weld area. The interface between the two metal sheets becomes heated sufficiently to weld the two sheets together at a small spot in the vicinity of the two electrodes.
The common application for spot welding is in automobiles where fender quarter panels or other body parts are secured to structural members. It is often necessary to remove these panels, such as when an automobile must be repaired following an accident.
In addition to removal of panels for repair or replacement following an accident, it is often necessary to remove an undamaged panel from an automobile that is being salvaged. After removal, the panel is then substituted for a panel that has been damaged.
While hood panels are typically removed by using an air chisel, grinder, or drill bit, in order to minimize damage to the parts involved, it is desirable to drill through one of the two fastened parts only to the depth of the facing surfaces between the two parts. In this way only one of the parts is damaged by the drill and the other remains substantially intact.
Metal is a difficult material to drill through and frequently the spot welds are positioned in inconvenient, hard-to-get-at locations. It can thus be quite difficult to drill through the spot weld interface without drilling at least part way through the second panel. The problem becomes even worse when relatively unskilled labor is used to perform the drilling operation.
To provide a relatively long drill life it is desirable to provide a high cutting pressure, i.e., about 100-120 pounds. This is difficult for a person to sustain if he can only use his own muscle to provide this cutting pressure.
It is also highly desirable to have a depth stop that can control the depth of the drilling operation. Wielander Schill, a German company, discloses the use of a C-arm assembly with a spot weld remover drill. The C-arm has a leg that is hooked over the back side of the panel joint and provides the action for the cutting pressure. Thus, control of the depth of the drilling operation may be maintained. However, the user must still provide significant muscle in providing sufficient cutting pressure for the drill bit.